Directional sonar system



y 969 E.A. GRANFORS ET AL 3,444,508

DIRECTIONAL SONAR SYSTEM Filed Sept. 8, 1967 BATTERY TIG.2

INVENTORS ERNEST A. GRANFORS v I E RL ES F S$EE HA l 1 47 HARRY w. KOANEK y 1969 E. A. GRANFORS ET AL 3,444,508

DIRECTIONAL SONAR SYSTEM Sheet Filed Sept. 8, 1967 INVENTORS ERNEST A.GRANFORS DON L. LOVELESS CHARLES F. BOYLE HARRY W. KO PANEK 1 BY I E MMMay 13, 1969 Filed Sept. 8, 1967 E. Av GRANFORS ET AL DIRECTIONAL SONARSYSTEM n U I;

2 O I I o r- U I I HQ l I l I J i I I M I x 0 L I i r.

l 0 I 19 I OJ I I z I I I 3 w' I I h .4 I x I L R I'"'"' I r I I Q A Q Ix I 9 "J I \Q I ERNEST A GRANF i DON L. LOVELESS I I EK Q x 3 l J BY May13, 1969 E. Av GRANFORS ET AL DIRECTIONAL SONAR SYSTEM Filed Sept. 8,1967 Ouvu FIG. 5

COMMON Y 5 0 x BY DIRECTIONAL 3/ A T1691 +0 I Sheet of5 n MooE 3/ TIGQco o y A. MODE INVENTORS ERNEST A. GRANFORS DON L. LOVELESS CHARLES F.BOYLE HAfiY W. KOMm May 13, 1969 E. A. GRANFORS ET AL DIRECTIONAL SONARSYSTEM Filed Sept. 8, 196'? Sheet 1 lllllllllll II s 2 5 LAP M 5 w E a cm A w v A Z W WW m U A A s R L m N I] N R Q L W 9 w E m /+i/ w XN s m M.T T M m I? m A 7 T R R A Wm m i u c \E 2 m m mw V lllllllllll l| omINVENTORS ERNEST A. GRANFORS DON L. LOVELESS CHARLES F. BOYLE PANEKHARRY W. K BYD United States Patent 3,444,508 DIRECTIONAL SONAR SYSTEMErnest A. Granfors, Don L. Loveless, and Charles F. Boyle, Jackson,Mich., and Harry W. Kompanek, Santa Barbara, Calif., assignors toSparton Corporation, Jackson, Mich., a corporation of Ohio Filed Sept.8, 1967, Ser. No. 666,405 Int. Cl. G015 1/72 US. Cl. 340-2 13 ClaimsABSTRACT OF THE DISCLOSURE An underwater acoustic sensing systemcomprising a command activated floating buoy assembly connected to asubmerged active electronic probe assembly containing hollowpiezoelectric ceramic cylinders stacked in a vertical interstitialarray. Three transducer sections are utilized having an output level andrelative polarity related in accordance with the direction from whichthe acoustic signal being received arrives. One of the acousticreceiving patterns is omnidirectional, and the others are sine-cosinedipole patterns which have the char acteristic of output level variationwith bearing. The omni output provides an amplitude and phase. referencefor comparing the amplitude and polarities of the two bearing-sensitivesignals. The resultant three signals, and compass information constitutethe primary outputs of the sensing system which are transmitted tosuitable decoding and radio transmission apparatus.

Background of the invention In the detection of underwater bodies anumber of methods have been employed, and depending upon the specificneeds, the most successful methods have relied upon one or more of thefollowing: magnetic (selfgenerated and perturbation of the earthsmagnetic field), optical, electrical field, thermal (infrared),hydrodynamical and acoustic (radiated self noise and reflected energy).Of these various methods the latter is the subject of the instantinvention. As utilized herein, sonal refers broadly to the employment ofpropagated acoustic energy through a water medium, for the purpose ofobservation, detection and/or communication.

As in other detection systems, one of the principal items of concern isto provide for an effective method of separating information indicatingthe presence of the sought object from the background or clutter causedby similar pieces of information completely unrelated to the detectedobject. Specifically, a passive sonar system attempts to do this usingacoustic signals which are radiated by the submerged body, and in theinstant case, broadly defined as an active system, the acoustic energy(signals) are reflected from the target. The acoustic energy is derivedprincipally from the sonar system transducer. In general, there areother sounces of acoustic energy in the ocean "which tend to mask thedesired signals. A great deal depends upon a quantity known assignal-to-noise ratio In this ration, (S) is the average signal power inwatts measured over the time it exists and (N) is called the averagenoise power in watts in the band of the sonar referring to the averagepower in the interfering background wave form. The signal and noisepowers are the unit area values in the water just outside thetransducer. Generally, it is assumed that a signal may be detected onthe average 50 percent of the time in the presence of noise if thesignal-to-noise ratio exceeds a predetermined number which is commonlyreferred to as the ice.

recognition differential. The applicants have found that by providingadditional selectivity in the form of directional horizontal and/ orvertical receiving responses, they achieve a significant enhancement ofthe signal-to-noise ratio as compared to even the most sophisticated andtechnically advanced equipment heretofore known.

While the instant invention may be utilized very effectively in apassive sonar system, it is intended to relate more specifically in anillustrative sense as an active sonar system wherein acoustic energy istransmitted by the sonar system and the signal is received by the systemin the form of an echo from the submerged body.

The invention relates to underwater sensing systems, and moreparticularly to sonar transducer systems for detecting submerged bodies,and includes a subsurface assembly consisting of a sonar transmitter,sonar receiver, and a transducer which is mechanically and electricallyconnected to the surface unit by a mechanically supporting electricallyconducting cable. The surface unit which supports the subsurface sensingunit when it is deployed in the sea water, contains a receiver, decoder,transmitter, an antenna system, and associated electronic equipment.

The command activated sonar system of the invention may be used as areplacement for existing air-launched sonar systems which are activatedupon water entry. This system can be operated and controlled as to pulsetype, rate, operating time and as to other operational characteristicsof the system, and thereby provides for a significant improvement in theflexibility of active sonar systems.

Previous attempts to provide for an effective submerged body detectionsystem involve utilization of magnetostrictive transducers as disclosedby Peek, US. Patent No. 2,468,837. More recent attempts to provide fordetection systems take advantage of piezoelectric transducers of thetype wherein the mechanical and electrical elements form periodic delaylines as described by Trott, US. Patent No. 3,321,738; and another typeemploys flexural-extensional electromechanical transducers foromnidirectional applications as disclosed by Toulis, US. Patent No.3,277,433. A still "further sonar system is disclosed by Ehrlich et al.,3,290,646, wherein is described a multimode transducer which producestwo simultaneous dipole patterns with substantially mutuallyperpendicular acoustic axes and an omnidirectional pattern from planewave signals, these pattern formations being provided by utilization ofexternal phasing and summing electronic circuitry which are essential tothe operation thereof.

Prior art active transducer systems have been limited respecting poweroutput and therefore range and accuracy. Other deficiencies in prior artsensing systems include limited functionality at high unit cost. Presentday high search rate requirements dictate the providing of highersensitivity and higher range detection systems, in conjunction withhigher resolution transducers as a subsystem with fully automated signalanalyzers and display units, as is now made possible by the instantinvention.

Summary of the invention It is the purpose of the invention to providefor a high resolution underwater detection system which makes possibleairborne fixed wing aircraft, helicopter, and shipboard detection andtracking of submerged objects. It has been found that a significantimprovement in such detection systems can be realized through the hereinprovided novel transducer assembly taken in conjunction with appropriatesignal conditioning and analyzing equipments. Enhanced directionalcapability, lower operating frequencies, and greater range are alsoprovided by the 3 instant system. Other significant advantages are itsinherent simplicity and low unit manufactured cost.

The instant invention provides for integral transducer phasing andsumming thereby directly providing for sinecosine voltage outputs.External cincuitry is eliminated.

Precise tracking and localization of submerged bodies is made possiblethrough the system wherein from the ship or aircraft address and sonictone information are supplied by a signal generator to a functiongenerator which then initiates an amplitude modulated radio frequencytransmission from a transmitter. T his UHF transmission is thendemodulated by a receiver in the floating surface assembly. Thereafterthe demodulated sonic pulse is sent to its sonar transmitter and then tothe transducer for ensonification of the water. After the sonictransmission is completed, the water units return to a listening modeuntil the next sonic transmission. Acoustic information received duringthe listening time is amplified by the sonar band pass receiver and theamplified information then frequency modulates a VHF transmitter whichtransmits on one of the selected VHF surface assembly frequencies. TheVHF transmission is received by the shipboard, avionic, or land basereceiver and is demodulated, in the receiver, with the demodulatedacoustic signal being sent to a signal generator for translation to alower frequency. The signal is sent to an analyzer and then presented ona display unit or as desired in the form of hard or soft copy output.

It has accordingly been realized that by utilizing the instantinvention, a significant improvement in water detection methods has beenmade possible. These functional benefits have been realized withoutincreasing system cost. Moreover, since integral phasing and summing ofvoltages is provided within the transducer array, a significantreduction in electronics has been realized while simultaneouslyproviding for higher resolution.

Accordingly, the principal object of this invention is to provide for animproved underwater sonar system.

Another object of the instant invention is to provide for a directionalsonar transducer having integral phasing and summing features.

Another object is to provide a multimode interstitial transducer arraywhich produces output voltages as a function of target bearing.

A still further object of the invention is to make commerciallyavailable a practical broad frequency sonar transducer system havingextreme sensitivity at 6 kc. to 12 kc., and being particularly usefulover the frequency range of cycles to 12 kc.

An additional object is to provide for the practical realization of adata command controlled underwater search system having highly sensitivedirectional capabilities.

Another principal object of the invention is to provide for a highcapacitance radially polarized cylindrical transducer having highdirectional sensitivity.

A particularly important object of the invention is to make possible avertically stabilized underwater cylindrical probe with high trackingfunctionality.

A further principal object of the invention is to make commerciallypractical the fully automated generation, transmission, analysis anddisplay of high signal-to-noise ratio directional sonar searchinformation.

These and other objects of the instant invention can be more readilyunderstood, and the uniqueness of the underwater detection system andmore particularly the transducer subsystem, as well as its manner ofconstruction and use, will be more readily appreciated from thefollowing detailed description, taken in conjunction with theaccompanying drawings, forming a part hereof, in which:

Brief description of the drawings FIGURE 1 is a representation of adeployed surface assembly and subsurface probe assembly;

FIGURE 2 is an exploded perspective of the subsurface probe assembly;

FIGURE 3 is a side perspective of the subsurface as,- semblyillustrating the fin stabilizer and towing bridle;

FIGURE 4 represents a top cross-sectional view of the transducerassembly taken along lines IVIV of FIG. 5;

FIGURE 5 is a side elevation view of the interstitial transducer arrayenclosed in an acoustically transparent neoprene boot;

FIGURE 6 depicts the omnidirectional array circuit equivalent;

FIGURE 7 represents the circuit equivalent of the directional linearray;

FIGURE 8 is a wiring diagram of the transducer interstitial array;

FIGURES 9a, 9b, 9c, and 9d illustrate an excited segmented transducercylinder section; and

FIGURE 10 shows the signal flow paths and operations of the system.

Suspended by cable 21 is the deployed subsurface probe assembly 1 asillustrated in FIG. 1. Positioned on top of floating buoy assembly 50 isa flotation bag 51 which houses the VHF antenna structure, and locatedwithin the floating assembly 50 is the electronic circuitry and otherfunctional electronic elements as illustrated in FIG. 10. Also shown inFIG. 1 are the stabilizing fins 2 which assume when stowed a nestedposition in a narrow annular space surrounding the body portion, butwhen deployed assume the open illustrated position. The towing bridlecable 3 and bridle spreader 4, taken in conjunction with bridleattachment band 5 located at the center of the horizontal fluid dynamicdrag of the subsurface probe, make possible stabilization about thevertical axis of the probe 1 despite the action of currents andimpressed fluid flow thereupon. More particularly, the fin and bridlesystem act by means of a dihedral effect to constrain the probe assemblyto align itself in a single vertical attitude referenced to thedirection of an impressed fluid flow.

It is thus seen that the bridle and fin structure cooperate to stabilizethe cylindrical probe to maintain a vertical attitude thereto while itis under the influence of steady state transverse fluid flow conditionsof any speed, with the fins and bridle assembly further acting toincrease the righting moment of the body, thus causing it to maintain avertical attitude under other conditions which might produce disturbingforces, such as under conditions of vertical heaving motion. Byminimizing yaw and roll of the probe, accurate transducer responsepatterns and transducer resolution are made possible.

In FIG. 2 is an exploded perspective of the subsurface probe assemblyillustrating the major arts thereof, with the transducer interstitialarray 10 supported between aluminium flanged cylinders 11 and 12 andmounted below the cable pack housing 13. Contained in the upper aluminumcylinder is a battery 14, and within the lower aluminum supportingcylinder 12 is contained a multisectioned electronic section 15 suitablyenclosed and sealed therein by bottom plate 16 and screws 17.

As illustrated in FIG. 3, the electronic section 15 and batterycompartment 14 are located within the area defined by a transduceraluminum cylinder 11 and 12 supporting members. Also shown in FIG. 3 isthe lower bridle cable 3 attachment to probe 1 located at point 18within the lower plate 16. Located generally at 15 are the poweramplifier, compass circuitry, compass sensor, sonar transmitter,transmitter-receive relay and multiplexer, heat sink, multichannelamplifier, as well as the sonar receivers. Immediately to the exteriorof aluminum separating and supporting cylinders 11 and 12 is the ceramictransducer array 10, as shown in FIG. 4.

As illustrated by FIG. 4, a cross section taken along IVIV of FIG. 5,the piezoelectric ceramic 31 (lead zirconate-lead titanate) is providedwith an annular air space 32 between Delrin spacer 33 which alsoprovides structural rigidity and support thereto, with the aluminum can12 being suitably end sealed by metal cap 35. While PZT ceramics asmanufactured by Clevite Corporation, Bedford, Ohio, have been foundparticularly useful, other piezoelectric materials can be desirablyemployed such as ADP, lithium sulphate, and other polycrystallinematerials.

Making electrical connection to the silver film 37 along the exterior ofceramic cylinder elements 31 are contacts 36 with electrical contacts 38being provided for contact to inner silver electrode areas 37b. Theelectrode configuration of FIG. 4 is as employed in the directionaltransducer cylindrical elements. The electrical connections are madebetween opposing quadrants of the interior positioned electrodes 38.External connections are made as illustrated to the X, Y, and common, asillustrated in FIG. -8. Providing for a completely sealed enclosure isthe neoprene boot 39. Full cylinders with full Ag electrode areas (innerand outer surfaces) function as the omnidirectional elements.

The individual ceramic cylindrical elements 31 are identified withnumbers from 1 to 11 as illustrated in FIG. 5. These correspondingindividual functional electrical elements are identified in FIG. 6 andFIG. 7. As illustrated, they can be represented as capacitive elements.In FIG. 6 and FIG. 7 shading capacitors 50 are employed. Thesecapacitors are typically metalized Mylar. Also shown in FIG. 5 are thesilver plated outer electrode 37 areas, neoprene protective coating 39,with aluminum cylinder and flange supports 11 and 12. The Delrin spacerand support 33 has disposed contiguous therewith synthetic cork shims33a to provide the cushioning and sealing thereat. Use of acousticisolator shims 33a between the spacer 33 and the cylindrical ceramicelements 31 are necessary for proper transducer functioning. WhileCorprene, a mixture of cork and neoprene, has been found useful, otheracoustic isolating materials can be employed. Elements 31 areselectively spaced to provide minimal pertabations occurring in themajor beam pattern and to also promote maximum. reduction of minorlobes.

A wiring diagram is shown in FIG. 8 for the transducer element andillustrates the electrical phase relationship between the omnielements31 (odd numbered units) and the electrical phase relationship betweenthe directional elements 31 (even numbered units). The simplicity of thecircuitry lends itself for low cost manufacture and also provides forinherent functional accuracy and reliability. No external phasing orcomplicated summing circuitry are required to achieve the directionalcharacteristics. Shading capacitors 50 providing for a reduction ofundesired minor lobes are typically of the metalized Mylar type.

The directional properties of the interstitial cylindrical transducerassembly result from the fundamental that any right circular cylinderhas several mechanical modes of resonance. In the case of the segmentedcylinder, the output is the sum of two voltages, both of which are theresult of vibrations in two principal modes as noted herein (FIGS. 91:,9b, 9c, and 9d). When a pressure wave passes the cylindrical element 31,radial expansions and contractions occur. If all the stresses andvoltages developed are in phase, the transducer is vibrating in the nmode as in FIG. 9b. The transducer has many resonant modes having thefollowing frequency relationship:

where:

f =reson ant frequency D=diameter of cylinder C=sound velocity withinthe material n=mode of vibration.

Unless otherwise suppressed, the cylinder when mechanically driven willresonate in several modes simultaneously. When placed in a sound fieldthe nodes of vibration of the cylinder will be aligned tangentially tothe equal-pressure plane of the sound wave, or in other words,perpendicular to the sound source. Thus, for 11:0, the cylinder willvibrate in a radial mode (FIG. 9b) yielding an omnidirectionalhorizontal directivity pattern. For 11 1, the cylinder will vibrate in adipole mode (FIG. 9a yielding essentially a cosine directivity pattern.The formula for the resonance of a right cylinder as expressed in theequation may be referred to as the mechanical resonance of the cylinderelements 31. The significance of the mechanical resonance of thetransducer elements 31 is in the manner in which the resonant frequencyrelates to the electromechanical coupling coefficient of thepiezoelectric elements per se. When placed in a sound field, the closerto the resonant frequency that the sound source is operated, the greaterthe mechanical to electrical transformation of energy is realized withattendant higher transducer efliciency. By practicing the invention, theapplicants have observed that the instant transducer system soundpressure sensitivity is very high throughout the frequency range of from5 cycles to 12 kilocycles, and that it is particularly efficient andsensitive in the frequency range from 6 kc. to 12 kc. Moreover, theapplicants have found that their system may be operated at frequenciessubstantially removed from the resonant frequency with a correspondingpenalty in terms of electroacoustic efliciency, but not necessarily acorresponding change in the sound pressure-toaoutput voltagerelationship or pressure sensitivity. Consequently, a useful voltageoutput may be achieved from transducer 10 at frequencies as low as 5cycles without significant pattern degradation in either theomnidirectional or directional modes of operation.

In a more detailed manner FIG. 9c and FIG. 9d represent the stress of apiezoelectric transducer cylinder 31 excited in the n, mode. As shown inFIG. 9d the upper half of the cylinder is stressed in one radialdirection, while the lower half is stressed in the opposite radialdirection. At points midway between these two halves the tangentialstress is maximum while the radial component is zero. Because theelement is sensitive only to radial stressing, a voltage will not bedeveloped at the nodes, as illustrated by FIG. 9c. While absolutepressure activates the n mode, the pressure gradient is the motivatinginfluence of the n mode. The pressure gradient of a sonic wave isdegrees out of phase with the absolute pressure of that wave. Therefore,the voltage developed in an individual element due to the In mode is 90degrees out of phase with the voltage developed by stresses of the nmode.

The output of one element of the segmented cylinder is the sum of the nand n voltages. To separate the two voltages to obtain the signaldeveloped in the n mode, the outputs of the two opposite elements mustbe subtracted. The voltage produced in the n mode in all elements isequal in amplitude and phase. Thus, there will be no difference and nooutput due to vibration in this particular mode.

The n mode of vibration generates voltages in opposite elements that areequal in amplitude and degrees out of phase. Therefore, the differencetaken between opposite elements produces an output equal to the sum ofthe independent elements. If four equally-spaced electrodes are employedas illustrated in FIG. 4, it is possible to combine the voltage outputsas indicated to provide for two separate channels yielding sine/cosinepatterns (spatially at right angles to each other). This is the responseherein provided.

Applicants have found that by utilizing radial (through the cylinderwall thickness) polarization a significant increase in element capacityand sensitivity is realizable. These gains are provided by the use ofthin wall ceramic cylinders, ordinarily impractical when using otherforms of polarization. In other poling techniques, such as in tangentialpolarization, thin wall elements may not be readily employed as apractical matter because of the destructive elfects resulting from thesevere mechanical stresses incurred in the poling process. Inasmuch as40,000 volts/ cm. is typically used in polarizing ceramics, therelatively large electrode spacing, and small dielectric cross sectionalarea introduces severe mechanical stresses in the material. However,when poled through the cylinder wall thickness, damage is minimizedwhile obtaining a more uniform potential gradient during the polingprocess. By utilizing thin wall cylinders, applicantsrealize highcapacitance values with electrode spacing being wall thickness. In othermethods of poling where large sections of the ceramic are involved thelikelihood of obtaining ceramic chemical, mechanical and electricaluniformity throughout the entire volume involved is quite low and hencecosts of manufacture are significantly greater due to poor yields.

The applicants have minimized the problem of transducer elementnonuniformity and have thereby significantly reduced their manufacturedcost. More significant is the element uniformity now possible betweenopposed element quadrants and the resultant increased element quadrantcapacities and increased voltage sensitivity. It is imperative for highsensitivity and pattern symmetry that the opposing quadrants of therespective directional transducer elements be electrically substantiallyidentical, and this has now been made possible by the instant invention.The ceramic polarization and electrode configura tion enable a level ofsynergism in results not heretofore possible, particularly when taken inconjunction with the stabilized probe for underwater search operations.

The underwater transducer assembly of the instant invention is acomposite unit consisting of cylindrical elements 31 which provide foromnidirectional and directional operations. As illustrated in FIG. 5,the elements 31 are positioned so that each directional transducerelement (even numbered units) is disposed between an omnidirectionalelement, and separated therefrom by neoprene or another suitableacoustic isolator 33a. It has been found that mechanical rigidity andease of manufacture can be enhanced by employing a plastic separator 33in conjunction with the acoustic isolator 33a. The piezoelectric ceramic(as shown in FIG. elements 1, 3, 5, 7, 9, and 11, are omnidirectionalunits which are employed for both transmission and reception. Interposedbetween these are segmented receiving (or alternately transmitting ifdesired) units consisting of functional sections as shownin FIG. 4,which have sine-cosine described directional responses. The sinedescribed directional response for the X channel being substantiallydisposed in a horizontal plane and the cosine directional response forthe Y channel being similarly disposed in the horizontal plane as shownby FIG. 10. Experimental results have verified that the patterns are notsignificantly effected by frequency of operation. When connected foroperation in the omnimode, the system has been found to respond towithin 1 db. total variation throughout the angular range.

In FIG. 10 wherein is shown the signal flow and operations for thesurface and subsurface sections of the search and tracking system it canbe seen that the composite command and sonic signal conveyed by UHFtransmission from the command transmitter enters the surface assemblyand is duplexed to the UHF receiver. The command is sent to a decoderafter demodulation by the receiver. The decoder inhibits all signalsexcept the desired address tone combination. Under this condition thedecoder allows the sonic signal to pass on to activate the T/R relaysfor the transmit condition. The signal which follows the address isrequired to hold the relays in the transmit condition. All the addresssignals, therefore, must be present in a given sequence to permittransmission of a sonar pulse.

Following the signal (FIG. 10) from the surface unit down the cable tothe subsurface assembly, it passes through the T/R relay where it isamplified and applied to the omni sections of the transducer throughanother T/R relay. The water is ensonified by the sonar pulse (appliedsignal). When the sonic signal from the command transmitter drops out,the T/R relays revert to their receiving mode. The incoming signal issensed in three different ways by the transducer. The output level andrelative polarity of each of the three transducer sections are relatedin accordance with the direction from which the acoustic signal arrives.Since the incident pressure wave is in the same relative phase for allthree sections, the output relationships then, are dependent on thetransducer characteristics, as hereinabove noted. The

acoustic receiving patterns are shown at the transducer in the lowerportion of FIG. 10; one being omnidirectional and is labeled as aconvenience in showing relative phase at an instant when the receivedpressure is at a positive peak. The others are sine-cosine dipolepatterns which have the characteristic of output level variation withbearing. As bearing varies, the output signal phase changes alternatelyfrom in-phase 5+ to phase opposition as the output diminishes, passesthrough zero and increases again.

The omnioutput, having constant level and phase regardless of bearing,provides an amplitude and phase reference for comparing the amplitudeand polarities of the two bearing-sensitive signals. Because the dipoleresponses are spatially orthogonal, the information inherent in thethree signals is sufficient to deduce bearing. These three signals andcompass information are the primary inputs. Compass and sonicinformation from the three channels are multiplexed for transmission upthe cable, with the data being presented to a VHF transmitter andradiated.

A flux gate compass has been found particularly useful to provide thebearing reference to magnetic north. This operates on a magnetic coresaturation principle and utilizes a common core with toroidal winding toachieve greater uniformity between reactors. It permits directtransmittal of the outpu signals obviating the need to translate theoutput frequencies to conserve multiplexing signal band width.

As hereinabove disclosed, a significant advance in the art has beenprovided inasmuch as applicants make possible integral transducerphasing and summing with direct (sine-cosine) target bearing-relatedvoltage outputs. Typically, the output of the directional transducer canbe represented by the following response patterns:

It is thus seen that the signal voltage output of the transducer withthe response pattern represented by (x) is:

S =A cos 0 The output of the complementary pattern (y) is:

Is /=14 sin 0 The coefiicient A is indicative of the sound intensitylevel at the probe 1 location, and the value A of course assume the samevalue in both equations since the transducer is sensitivity respectingboth paterns is the same. This level of directional informationsimplicity is made possible by the inventive concept through theaccuracy provided integrally Within the transducer interstitial arrayand its synergetically related probe stabilization system. Uniquelycooperating with the probe 1 the fin and bridal assembly stabilizationsystem make possible greater target bearing detenm-inations nototherwise obtainable because of the surrounding dynamic fluid forceswhich would otherwise introduce errors. Compass information would suffersignificantly as would the absolute accuracy of the directional beampatterns, particularly respecting amplitude.

For target elevation determinations multiple delay lines can be employedin voltage phasing and summing of interstitial element outputs toprovide vertical beam steerage (target depth and discrimination againstbottom/surface reverberation). Alternately, the applicants have foundthat by horizontally deploying a multimode transducer (havingfunctionally at least one omni and one directional element), the uniteither independently or suspended with a vertically aligned probe, canbe used to scan in the vertical plane and thereby generate target depthinformation. This type of scanning taken in conjunction with horizontalscanning (as hereinbefore described) makes possible a substantiallyincreased amount of tracking information.

Applicants not only provide for submerged body detection but alsoprovide for securing meaningful directional target information under allsea states with a high degree of accuracy over the full 360 traverse,over a wide frequency range, and with good range. The basic inventiveconcept also makes possible high capacitance (inherently smalldielectric spacing and large effective electrode areas) with ease ofpoling while minimizing cost. If desired, the instant system can also beemployed strictly as a highly sensitive directional passive system withthe dipole pattern (X and Y axes) and the reference voltage (omni) beingprovided by the array elements 31. For certain uses a direct cable linkfrom the buoy to a vessel or aircraft may be desirably employed. Anotheralternative technique inherent in the instant concept is that whichcould lend itself to more economical signal processing for the purposeof establishing target bearing; namely, it may be desirable in theconstruction of the cylindrical array (FIG. to progressively stagger(along a surface chord parallel with vertical probe axis) or skew thedirectional elements with reference to their respective horizontalmaximum sensitivity coordinates such that each individual sinecosinepair is oriented at a different azimuthal bearing angle, which willthereby enable each directional element of the array (interstitial withomni or array with all directional and modified interior electrodefunctionality) to be sequentially or continuously scanned for discretetarget information.

It is thus apparent to those skilled in the art that variousmodifications of the invention can be made \without departing from theconcept hereof, and since various changes can be readily made as amatter of choice or desire, it is intended that all matter containedherein shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An acoustic underwater search system comprising, in combination,

(a) a submerged cylindrical probe,

(b) a floatable surface assembly,

(c) cable ime-ans interconnecting said probe and said surface assembly,

((1) a stabilizer attached to said probe, said stabilizer providingvertical attitude alignment referenced to impressed fluid flow directionagainst said probe,

(e) bridle means attached at one end thereof to said probe and attachedat another end thereof to said interconnecting cable means,

(f) multimode electromechanical transducer means contained within saidprobe, and

(g) plane wave signal receiving, conditioning, and

transmitting means contained within said surface assembly.

2. An acoustic system as in claim 1 wherein said multimode transducermeans comprises at least one directional cylindrical piezoelectricelement.

3. An acoustic system as in claim 2 wherein said element is providedwith electrode areas along its internal and external cylindricalsurfaces.

4. An acoustic system as in claim 3 wherein is provided at least twopair of functionally equal and opposite electrodes.

5. An acoustic system as in claim 1 wherein said bridle means isattached atone end thereof to said probe at the end points of theexterior surface chord located substantially at the transverse dragcenter of said probe, and attached at another end thereof to saidinterconnecting cable means.

6. An acoutic system as in claim 5 wherein said probe stabilizercomprises a fin assembly having major functional surfaces alignedsubstantially parallel to the longitudinal axis of the probe.

7. An acoustic system as in claim 2 wherein is provided at least oneomnidirectional cylindrical piezoelectric element.

8. An acoustic system as in claim 2 wherein said piezoelectric elementis radially polarized.

9. An acoustic system as in claim 7 wherein multiple omnidirectional anddirectional elements are provided and stacked in a plane perpendicularto the major surfaces thereof, with said directional elements beingdisposed between and acoustically isolated from said omnidirectionalelements thereby providing an interstitial array.

10. An acoustic system as in claim 2 wherein said multimode transducerintegrally provides directional acoustical responses.

11. A directional sonar system comprising, in combination,

(a) probe means containing an electromechanical transducer and a powersupply,

(b) a buoy containing electrical signal receiving, conditioning andtransmitting means,

(c) cable means electrically connecting said probe means and said buoy,

(d) a support,

(e) said transducer comprising cylindrical piezoelectric elementsmounted on said support,

(f) transducer input and output means,

said transducer output and input means consisting essentially ofdirectional elements having paired quadrature electrodes, andomnidirectional elements having singularly paired electrodes,

(g) bearing information supply means,

(h) multiple shading capacitors, and

(i) electrical interconnections between said power supply, saidpiezoelectric elements, said bearing information supply means, saidcapacitors, and said buoy.

12. The directional sonar system of claim 11 wherein said bearinginformation supply means comprises a compass.

13. The directional sonar system of claim 11 wherein the transduceromnidirectional element voltage outputs and directional element voltageoutputs are directed to shading capacitors and summed to provide abearing related voltage output having a substantial vertical componentof directivity, said voltage being supplied to said buoy.

References Cited UNITED STATES PATENTS 3,093,808 6/1963 Tatnall et a1340-2 3,116,471 12/1963 Coop 340-2 3,176,262 3/1965 Ehrlich et a1. 340-3RICHARD A. FARLEY, Primary Examiner.

US. Cl. X.R. 340--3, 6, 10

